Mount public NAS: mount.cifs: permission denied

quick question:

Trying to auto-mount my Nas. I only use the public share (so don't need passwords) and I have followed this instruction: https://wiki.ubuntu.com/MountWindowsSharesPermanently

So this is the line I added to the fstab:

 //nas/public /media/public cifs guest,uid=janjanssen,iocharset=utf8 0 0

I do automount, but I don't have permission to access it. If I go in my network and manually mount(and log in with anonymous) it does work, and I have full access. So only the auto-mount doesn't work.

Does anyone have a solution?